The present invention relates to the combustion chambers of gas turbine engines and especially aviation turbine jet engines, and more precisely concerns a non-polluting combustion chamber arrangement.
Efforts have been made hitherto to improve the operation of combustion chambers, their reliability, their weight and other similar characteristics, without taking very much account however of pollution, except as regards the emission of visible smoke. Thus one has arrived at the conventional concept consisting in injecting the fuel into a primary combustion zone followed by a secondary combustion or dilution zone, the primary zone being arranged so that the richness of the fuel-air mixture may be close to the stoichiometric richness for the conditions of maximum continuous rating, and that its volume should be at least equal to the value necessary to ensure re-ignition in flight at a specific altitude. This conventional concept, from the pollution viewpoint, presents the following drawbacks:
On idling while the aircraft is stationary or taxying, by reason of the low mean richness of the primary zone, the combustion efficiency is not very good and a large quantity of carbon monoxide and unburnt hydrocarbons is ejected in the vicinity of the ground;
At the maximum continuous rating and on take-off, the combustion efficiency is close to the optimum but the design of the chamber implies a long stay of the gases in the zones where the richness of the mixture is substantially stoichiometric and the temperature achieved very high, by reason of this richness and of the high values of the temperature and pressure at the entry to this chamber, this being favorable to the production of various nitrogen oxides.